ENVIRONMENTAL IMPACTS OF COMBUSTION
TABLE OF CONTENTS
The negative effects of combustion on the environment – particularly greenhouse gas (GHG) emissions released to the atmosphere that contribute to global warming – have received much attention in recent years. This issue is addressed in the Kyoto Protocol (1997). Canada, which signed the Protocol, aims to reduce emissions between 2008 and 2012 by six percent of 1990 levels. Climate change resulting from global warming is one of the greatest challenges facing not only Canada but also the world. Managing combustion processes better and improving the efficiency of energy generation and use are two of the key strategies for reducing atmospheric emissions.
Therefore, this guidebook is being published in concert with Canadas policy on climate change as one of the tools for implementing it. Canadas goal of reducing GHG and acid-rain emissions can be met only with the co-operation of the owners and operators of combustion equipment. It is beyond the scope of this guidebook to describe the emissions in detail. Instead, a brief ove rv i ew is presented (see Table 2 for a list of some emissions from combustion systems and their effects). More complete information can be obtained from An Energy Efficiency and Environment Primer for Boilers and Heaters.
|EMISSION||SOURCE||EFFECT||GHG POTENTIAL RELATIVE TO CO2|
|CO2 (carbon dioxide)||Complete combustion of carbon in fuel||Global warming||1|
|CO (carbon monoxide)||Incomplete combustion of carbon in fuel||Smog|
|SO2 (sulphur dioxide)||Combustion of sulphur in fuel||Smog, acid rain|
|NOx (nitrogen oxides)||By-product of most combustion processes||Acid rain|
|N2O (nitrous oxide)||By-product of some combustion processes||Global warming||310|
|VOCs (volatile organic compounds)||Leakage and evaporation of liquid fuels (from, e.g., vehicles, fuel tanks, fuel pumps, refineries, solvents from paints)||Smog|
|CH4 (methane)||Principal component of natural gas; leakage from gas wells, pipelines and distribution systems||Global warming||21|
|H2O (water vapour)||Combustion of hydrogen in fuel||Localized fog|
|Particulates (dust, soot, fumes)||Unburned or partially burned carbon and hydrocarbons; also ash and dirt in fuel||Smog|
|Trace elements||Impurities in fuel||Potential carcinogens|
|Halogenated compounds||Compounds in fuel or combustion air containing halogens (chlorine, fluorine, bromine and iodine)||Potential carcinogens, global warming||Up to 24 000|
|INPUT CAPACITY||NOX EMISSION LIMIT, g/GJ** AND PPM (AT 3% O2)***|
|10.5 TO 105 GJ/h (10 TO 100 MILLION Btu/h)||GREATER THAN 105 GJ/h (>100 MILLION Btu/h)|
|Natural gas||26 (49.6)||40 (76.3)|
|Distillate oil||40 (72.3)||50 (90.4)|
|Residual oil with less than 0.35% nitrogen||90 (162.7)||90 (162.7)|
|Residual oil with 0.35% or more nitrogen||110 (198.9)||125 (226.0)|
* Canadian Council of Ministers of the Environment
To correct ppm NOx to 3% O2: NOx at 3% O2 = [NOx measured x 17.9] / [20.9 - O2], where O2 is oxygen measured in flue gas, dry basis
To convert ppm NOx at 3% O2 to g/GJ: for natural gas, g/GJ = ppm / 1.907 for fuel oil, g/GJ = ppm / 1.808
|FUEL AND BOILER TYPE||TYPICAL NOX EMISSIONS (PPM AT 3% O2)|
|No. 2 oil||Firetube||70-140|
|No. 4 oil||Package watertube||160-310|
|No. 6 oil||Package watertube||200-360|
Although the other GHGs, unit for unit, are much more potent than CO2 in their effects, the latter is the most important GHG because of its volume. In 1997 it represented three-quarters of Canada's total emissions. Most of the CO2 is generated by the combustion of fuels, whether for residential, industrial, transportation or electric power generation purposes. So, applying energy efficiency measures that reduce fuel consumption is crucial to reducing CO2 emissions.
Fuel consumers face a double challenge. One is economic – to get the best value for their fuel budget. The other is environmental – to keep emissions low, at least within legislated limits. Fortunately, what benefits the first objective also benefits the second.
Higher limits are allowed for equipment with a proven higher efficiency than normal and which, therefore, burns less fuel. Provinces and territories are responsible for enforcement and may enact stricter limits. They also have responsibility for determining to what extent the guideline applies to boilers and heaters that are being modified or overhauled.
Emissions of sulphur dioxide (SO2) and nitrogen oxides (NOx) contribute to acid rain and, therefore, are also of concern. SO2 emissions are controlled by limiting the allowable sulphur content of the fuel, but NOx emissions can be reduced by manipulating the combustion process. Guidelines for new boilers and heaters are presented in Table 3, and An Energy Efficiency and Environmental Primer for Boilers and Heaters describes the strategies for complying with NOx regulations.
- Date modified: